Because they impair cell-mediated immunity, opiates have been implicated as a cofactor in the progression of HIV-1 infection in the injection drug use (IDU) population. However, little data are available regarding the impact of opiates on cellular defenses at critical sites of infection in AIDS, e.g., the central nervous system (CNS). In this application, experiments are proposed for testing the hypothesis that opiates modulate the function of microglia and astrocytes (the brain's immune cells) and thus promote the pathogenesis of HIV-1 and Toxoplasma gondii, two of the most important causes of CNS disease in AIDS patients. Because of studies showing that endogenous opioid peptides and cocaine share many of the immunomodulatory activities of morphine, these agents will also be investigated. Two approaches will be taken, one involving in vitro murine brain cell culture models and the other involving murine models of toxoplasmic encephalitis. The aims of the in vitro studies have evolved from preliminary studies demonstrating that morphine alters the production by microglia and astrocytes of two key classes of immune mediators: cytokines and free radicals. Purified neonatal murine microglial cells, purified astrocytes, or cocultures of these glial cells with neuronal cells will be used to characterize: 1) the effects of morphine, endogenous opioid peptides, and cocaine on cytokine release from microglia and astrocytes and on the generation of free radicals by microglia, 2) the influence of morphine, endogenous opioid peptides, and cocaine on microglia- and astrocyte-mediated neuronal cell injury, 3) the impact of morphine and cocaine on glial cell-induced upregulation of HIV- 1 expression in chronically infected promonocytic cells and the effect of these drugs on HIV-1-induced neurotoxicity, and 4) the effect of morphine on microglial cell defense against T. gondii and the influence of morphine on T. gondii-mediated neurotoxicity. The specific aim of the in vivo studies will be to characterize the effect of chronic morphine administration on CNS toxoplasmosis. For the in vitro studies, the immunomodulatory activities of endogenous opioids that are found within the brain will be studied by using opioid receptor agonists and antagonists that are highly selective for delta and kappa sites. The focus of the in vitro and in vivo studies, and the related methodologies, will be those cytokines (tumor necrosis factor-alpha, transforming growth factor-beta, interleukin[IL]-1, IL-6) and free radicals (superoxide, nitric oxide) implicated in the neuroimmunopathogenesis of HIV-1 or T. gondii. This research is a logical extension of our earlier work ont he effects of opiates and cocaine on peripheral immune cells to studies of immune cells of the brain, a principal target organ not only for drugs of abuse but also for HIV-1. The studies encompassed in the specific aims will contribute to our long-term objectives of understanding how opiates act as a cofactor in AIDS and of devising ways to interfere with the development of full-blown AIDS in the IDU population.